QUANTITY AND COMPOSITION OF THE BLOOD IN MAN 911 



complete saturation with ammonium sulphate or sodio-magnesium sulphate, 

 or in the crystalline form by slight acidification, as in Hopkins' method 

 described on p. 73. Serum albumen is soluble in distilled water. Its 

 solutions therefore can be dialysed indefinitely without any precipitation 

 taking place. 



THE GLOBULINS. The globulins of serum, known as paraglobulin or 

 serum globulin, are obtained by half -saturation with ammonium sulphate. 

 Their solutions in salt coagulate at about 75 C. Since globulin is insoluble 

 in distilled water, it is precipitated on dialysing serum against, distilled 

 water. The precipitate obtained in this way is not however so great in 

 extent as that obtained on half-saturation, and on this account the globulin 

 fraction of the serum proteins has been divided into two fractions, namely, 

 euglobulin, precipitable by dialysis, and 'pseudo-globulin, not precipitable by 

 dialysis, but thrown -down on half -saturation with ammonium sulphate. 



A thorough study of serum globulin by Hardy has shown that this body forms 

 adsorption combinations with acids, alkalies, or neutral salts. With acids and alkalies 

 the globulin forms ' salts ' which ionise in solution so that in an electric field the entire 

 mass of protein moves. These salts cannot be precipitated by dialysis. In them the 

 globulin acts much more strongly as an acid than as a base, so that a weak acid, such as 

 acetic acid, has a much smaller dissolving power over globulin than has the equivalent 

 amount of hydrochloric acid, and boracic acid has a very slight power indeed. The 

 weak basic character of globulin causes its salt in weak acids to undergo hydrolysis 

 with separation of globulin, so that in order to reach the -same grade of solution with 

 a weak acid as with a strong acid a great excess of the acid is necessary. Owing to the 

 much stronger acid character of globulin it is found that weak ammonia dissolves it 

 almost as well as strong alkalies. With neutral salts globulins form molecular com- 

 pounds which are soluble, but are readily decomposed by water with liberation of the 

 insoluble globulin. They are therefore stable only in the presence of a comparatively 

 large excess of salt. The globulins differ from the albumens of the serum in containing 

 constantly organic phosphorus as an integral part of their molecule. In all its solutions 

 globulin is present in large molecular aggregates, so that it is impossible to filter a globulin 

 solution through a porous clay cell. 



TflE CONDITION OF THE PROTEINS IN THE BLOOD SERUM 



Although it is easy by such simple means as the addition or removal 

 of neutral salts to separate one or -more different forms of protein from 

 serum, we have strong evidence that these proteins do not exist side by 

 side in the serum, but are combined to form what we may term serum 

 protein, which acts as a whole and differs in its qualities from many of 

 those of its constituent globulins or albumens. When a current is passed 

 through blood serum no movement of protein takes place (Hardy). Alkali 

 globulin therefore- cannot be present. Salt globulin might be assumed 

 to be present since it does not ionise in solution, but serum is not preci- 

 pitated by simple addition of acid, which would readily precipitate salt 

 globulin in alkaline solution. Moreover serum can be readily filtered 

 through a porous cell, and this method is adopted for obtaining it free 

 from contamination by micro-organisms. Globulin in any of its solutions 

 will not pass through a porous cell. If globulin be present as such in the 



